Kotlinでカスタムデータ型を作成する方法と応用例

data class User(val name: String, val age: Int, val email: String)

data class クラス名(val プロパティ名: 型, val プロパティ名: 型, ...)

data class User(val name: String, val age: Int, val email: String)

val user1 = User("Alice", 25, "alice@example.com")

enum class Enum名 {
    定数1, 定数2, 定数3, ...
}

enum class Day {
    SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY
}

val today = Day.MONDAY
println(today)  // 出力: MONDAY

enum class Day(val message: String) {
    SUNDAY("Relax, it's Sunday!"),
    MONDAY("Back to work!"),
    TUESDAY("Keep going!"),
    WEDNESDAY("Halfway through the week!"),
    THURSDAY("Almost there!"),
    FRIDAY("Weekend is near!"),
    SATURDAY("Enjoy your Saturday!")
}

fun main() {
    val today = Day.FRIDAY
    println(today.message)  // 出力: Weekend is near!
}

  for (day in Day.values()) {
      println(day)
  }
  // 出力:
  // SUNDAY
  // MONDAY
  // TUESDAY
  // ...

  println(Day.MONDAY.name)  // 出力: MONDAY

  println(Day.WEDNESDAY.ordinal)  // 出力: 3

enum class Status {
    SUCCESS, ERROR, LOADING
}

fun handleResponse(status: Status) {
    when (status) {
        Status.SUCCESS -> println("Operation succeeded.")
        Status.ERROR -> println("An error occurred.")
        Status.LOADING -> println("Loading, please wait...")
    }
}

fun main() {
    handleResponse(Status.LOADING)  // 出力: Loading, please wait...
}

sealed class クラス名 {
    class サブクラス名1 : クラス名()
    class サブクラス名2 : クラス名()
}

sealed class NetworkResult {
    data class Success(val data: String) : NetworkResult()
    data class Error(val message: String) : NetworkResult()
    object Loading : NetworkResult()
}

fun handleNetworkResult(result: NetworkResult) {
    when (result) {
        is NetworkResult.Success -> println("Data received: ${result.data}")
        is NetworkResult.Error -> println("Error occurred: ${result.message}")
        NetworkResult.Loading -> println("Loading...")
    }
}

fun main() {
    val success = NetworkResult.Success("User data")
    val error = NetworkResult.Error("Network error")
    val loading = NetworkResult.Loading

    handleNetworkResult(success)  // 出力: Data received: User data
    handleNetworkResult(error)    // 出力: Error occurred: Network error
    handleNetworkResult(loading)  // 出力: Loading...
}

sealed class AuthResult {
    data class Success(val userId: String) : AuthResult()
    data class Failure(val error: String) : AuthResult()
    object Loading : AuthResult()
}

data class Person(val name: String, val age: Int) {
    fun isAdult(): Boolean {
        return age >= 18
    }
}

fun main() {
    val person = Person("Alice", 20)
    println("${person.name} is adult: ${person.isAdult()}")  // 出力: Alice is adult: true
}

data class User(val firstName: String, val lastName: String) {
    val fullName: String
        get() = "$firstName $lastName"
}

fun main() {
    val user = User("John", "Doe")
    println("Full name: ${user.fullName}")  // 出力: Full name: John Doe
}

sealed class CalculationResult {
    data class Success(val value: Int) : CalculationResult() {
        fun display() = "Result: $value"
    }

    data class Error(val message: String) : CalculationResult() {
        fun display() = "Error: $message"
    }
}

fun main() {
    val success = CalculationResult.Success(42)
    val error = CalculationResult.Error("Division by zero")

    println(success.display())  // 出力: Result: 42
    println(error.display())    // 出力: Error: Division by zero
}

fun 型名.関数名(引数): 戻り値型 {
    // 関数の処理
}

fun String.addExclamation(): String {
    return this + "!"
}

fun main() {
    val message = "Hello"
    println(message.addExclamation())  // 出力: Hello!
}

data class Person(val name: String, val age: Int)

fun Person.greet(): String {
    return "Hello, my name is $name and I am $age years old."
}

fun main() {
    val person = Person("Alice", 25)
    println(person.greet())  // 出力: Hello, my name is Alice and I am 25 years old.
}

class Example {
    fun show() = "Member function"
}

fun Example.show() = "Extension function"

fun main() {
    val example = Example()
    println(example.show())  // 出力: Member function
}

dependencies {
    testImplementation("org.jetbrains.kotlin:kotlin-test-junit:1.9.0")
    testImplementation("junit:junit:4.13.2")
}

data class Person(val name: String, val age: Int) {
    fun isAdult(): Boolean {
        return age >= 18
    }
}

import org.junit.Assert.assertTrue
import org.junit.Assert.assertFalse
import org.junit.Test

class PersonTest {

    @Test
    fun `isAdult returns true when age is 18 or older`() {
        val adultPerson = Person("Alice", 20)
        assertTrue(adultPerson.isAdult())
    }

    @Test
    fun `isAdult returns false when age is under 18`() {
        val childPerson = Person("Bob", 16)
        assertFalse(childPerson.isAdult())
    }
}

./gradlew test

dependencies {
    testImplementation("io.kotest:kotest-runner-junit5:5.5.5")
}

import io.kotest.core.spec.style.StringSpec
import io.kotest.matchers.shouldBe

class PersonTest : StringSpec({
    "isAdult should return true for age 18 or older" {
        val adult = Person("Alice", 18)
        adult.isAdult() shouldBe true
    }

    "isAdult should return false for age under 18" {
        val child = Person("Bob", 17)
        child.isAdult() shouldBe false
    }
})

sealed class ApiResponse<out T> {
    data class Success<T>(val data: T) : ApiResponse<T>()
    data class Error(val message: String, val code: Int) : ApiResponse<Nothing>()
    object Loading : ApiResponse<Nothing>()
}

import kotlinx.coroutines.delay

suspend fun fetchUserData(userId: String): ApiResponse<String> {
    return try {
        // 擬似的なネットワーク遅延
        delay(2000)

        if (userId == "valid_user") {
            ApiResponse.Success("User data for $userId")
        } else {
            ApiResponse.Error("User not found", 404)
        }
    } catch (e: Exception) {
        ApiResponse.Error("Network error: ${e.message}", 500)
    }
}

fun handleApiResponse(response: ApiResponse<String>) {
    when (response) {
        is ApiResponse.Success -> {
            println("Data received: ${response.data}")
        }
        is ApiResponse.Error -> {
            println("Error ${response.code}: ${response.message}")
        }
        ApiResponse.Loading -> {
            println("Loading data...")
        }
    }
}

import kotlinx.coroutines.runBlocking

fun main() = runBlocking {
    println("Fetching user data...")
    handleApiResponse(ApiResponse.Loading)

    val response = fetchUserData("valid_user")
    handleApiResponse(response)

    val errorResponse = fetchUserData("invalid_user")
    handleApiResponse(errorResponse)
}

Fetching user data...
Loading data...
Data received: User data for valid_user
Error 404: User not found